Enthalpies of Formation of Compounds in the P₂O₅−CaO−H₂O System

Abstract

The enthalpies of formation were determined for Ca 4 (PO 4 ) 2 O, R-Ca 3 (PO 4 ) 2 , and the hydroxyapatite compositions Ca 10 (PO 4 ) 6 (OH) 2 and Ca 9 (HPO 4 )(PO 4 ) 5 OH by the analysis of isothermal calorimetric results obtained at 37.4°C. Both hydroxyapatite compositions were formed by reaction of Ca 4 (PO 4 ) 2 O with CaHPO 4 or with CaHPO 4 ‚ 2H 2 O in water depending on the molar proportions of the reactant used. Ca 9 (HPO 4 )(PO 4 ) 5 OH was also formed by direct hydrolysis of R-Ca 3 (PO 4 ) 2 in water. Enthalpy of formation values were calculated by a Hess's Law analysis using several sets of equations. In summary, the enthalpy of formation values are: for Ca 4 (PO 4 ) 2 O, -476 2.4 kJ/mol, for R-Ca 3 (PO 4 ) 2 , -409 6.5 kJ/mol, for Ca 9 (HPO 4 )(PO 4 ) 5 OH, -127 19.7 kJ/mol, and for Ca 10 -(PO 4 ) 6 (OH) 2 , -137 44.0 kJ/mol at 37.4°C.

Thermodynamic Assessment of the System CaO–P 2 O 5 : Application of the Ionic Two‐Sublattice Model to Glass‐Forming Melts

“…The value of Δ f H 0 298.15 of C4P phase resulting from the present assessment is −4904 kJ/mol, close to that suggested by Martin et al 68 The Gibbs energy changes of different reactions involving C4P, collected in Table II, were compared with the values calculated in the present work, in Fig. (1).…”

Thermodynamic Assessment of the System CaO–P 2 O 5 : Application of the Ionic Two‐Sublattice Model to Glass‐Forming Melts

“…The value of Δ f H 0 298.15 of C4P phase resulting from the present assessment is −4904 kJ/mol, close to that suggested by Martin et al 68 The Gibbs energy changes of different reactions involving C4P, collected in Table II, were compared with the values calculated in the present work, in Fig. (1).…”

Controlling the Reactivity of Calcium Phosphate Cements

“…Here, the factor that had the main effect on the overall duration of the setting reaction is the particle size: the use of ACP f decreased the overall setting duration by two orders of magnitude even if it did not markedly modify the time point of the reaction start (Fig 1). The total heat released during the transformation of α-TCP into CDHA is close to the values reported by Camiré et al (100 to 250 J/g with a value close to 150 J/g for a powder similar to that used here) 5 and by Martin et al (-133 kJ/mole CDHA = 140 J/g α-TCP) 3 .…”

Calcium Silicate Phases Explained by High-Temperature-Resistant Phosphate Probe Molecules

“…The frustrated chain vibrational mode disappears (Si–O systems react with CaO to form the C–S phase). After 1000 °C, PO 4 has again advanced into the structure because of the calcium gradient proposed by eq . The heat of formation of every compound was calculated, validating the series of reactions proposed for the product depicted in eq . , …”

Thermodynamic Assessment of the System CaO–P 2 O 5 : Application of the Ionic Two‐Sublattice Model to Glass‐Forming Melts

“…The value of Δ f H 0 298.15 of C4P phase resulting from the present assessment is −4904 kJ/mol, close to that suggested by Martin et al 68 The Gibbs energy changes of different reactions involving C4P, collected in Table II, were compared with the values calculated in the present work, in Fig. (1).…”

Controlling the Reactivity of Calcium Phosphate Cements

“…Here, the factor that had the main effect on the overall duration of the setting reaction is the particle size: the use of ACP f decreased the overall setting duration by two orders of magnitude even if it did not markedly modify the time point of the reaction start (Fig 1). The total heat released during the transformation of α-TCP into CDHA is close to the values reported by Camiré et al (100 to 250 J/g with a value close to 150 J/g for a powder similar to that used here) 5 and by Martin et al (-133 kJ/mole CDHA = 140 J/g α-TCP) 3 .…”

Calcium Silicate Phases Explained by High-Temperature-Resistant Phosphate Probe Molecules

“…The frustrated chain vibrational mode disappears (Si–O systems react with CaO to form the C–S phase). After 1000 °C, PO 4 has again advanced into the structure because of the calcium gradient proposed by eq . The heat of formation of every compound was calculated, validating the series of reactions proposed for the product depicted in eq . , …”

Thermodynamic Assessment of the System CaO–P 2 O 5 : Application of the Ionic Two‐Sublattice Model to Glass‐Forming Melts

“…The value of Δ f H 0 298.15 of C4P phase resulting from the present assessment is −4904 kJ/mol, close to that suggested by Martin et al 68 The Gibbs energy changes of different reactions involving C4P, collected in Table II, were compared with the values calculated in the present work, in Fig. (1).…”

Controlling the Reactivity of Calcium Phosphate Cements

“…Here, the factor that had the main effect on the overall duration of the setting reaction is the particle size: the use of ACP f decreased the overall setting duration by two orders of magnitude even if it did not markedly modify the time point of the reaction start (Fig 1). The total heat released during the transformation of α-TCP into CDHA is close to the values reported by Camiré et al (100 to 250 J/g with a value close to 150 J/g for a powder similar to that used here) 5 and by Martin et al (-133 kJ/mole CDHA = 140 J/g α-TCP) 3 .…”

Calcium Silicate Phases Explained by High-Temperature-Resistant Phosphate Probe Molecules

“…The frustrated chain vibrational mode disappears (Si–O systems react with CaO to form the C–S phase). After 1000 °C, PO 4 has again advanced into the structure because of the calcium gradient proposed by eq . The heat of formation of every compound was calculated, validating the series of reactions proposed for the product depicted in eq . , …”